Some advanced telecommunication services provided by a PBX often require the use of an adjunct connected over a telephone line to the PBX. These services may include auto attendant, call management, etc., and typically require an additional data link to be connected between the adjunct and the PBX. Unfortunately, the data link requires special and expensive interface hardware and software at the PBX and adjunct to provide the data communication therebetween. Moreover, since this data link requires a separate connection facility, it thereby reduces the reliability of the adjunct to PBX connection.